Polyethylene is used in large quantities in the packaging industry for the production of films and sheets, because the material shows low weight while at the same time presenting a particularly high mechanical strength, resistance to corrosion in the presence of moisture/water and oxygen, and extremely reliable long-term durability. Furthermore, polyethylene has good chemical resistance and is especially suited for raffia-applications, such as nettings, decorative tapes and mono-axially stretched films.
It is important that polyethylene tapes intended for raffia applications possess good tensile strength and elongation at break, since the tapes are subjected to high strains and stresses, for example during the production of nettings. Nevertheless, polyethylene compositions known in the art often show low processability, and in particular a narrow stretching window when the polyethylene sheet is subjected to stretching. The “stretching window” is defined by the gap between the minimum and the maximum stretching ratio of a polyethylene foil or band, wherein the minimum stretching ratio is the value below which undesired lumps appear in the foil/bands, and the maximum stretching ratio is the value above which the foil or band tends to rip during processing. The wider the stretching window, the more processable a polymer moulding composition, with advantages in both the production and the use of the composition.
Therefore, it would be desirable to provide polyethylene moulding grades possessing, besides good mechanical properties such tensile strength and elongation at break, also a wider stretching window and an improved processability, which would allow a high output from the extruder and a broad range of possible stretching ratio.